Yeah I went for it.
In terms of "all you can eat", yes - the offer lives up to its name. Every time they serve you a pizza, they ask you if you want more, and at that point you should say yes. SO by the time you're done eating your pizza, the waiter is already there with the next helping.
Also, an hour is actually more than you require to get a full stomach. Me and my friend left in about 45 minutes with tummies filled to the brim.
But in terms of quality of the pizza its not THAT great. Generally a Papa John's Pizza is pretty tasty. These ones are passable. I suppose you can compare it to the taste of a lukewarm Dominos pizza.
That said, its definitely worth a shot at least once, since on a per rupee basis, you actually get a huge quantity of decently good pizza.